M. S. Newman and H. A. Karnes, J. Org. Chem., 31, 3980 (1966) disclose that when certain O-aryl dialkylthiocarbamates are pyrolyzed, S-aryl dialkylthiocarbamates are obtained in high yields. They also reveal that the so-obtained S-aryl dialkylthiocarbamates are readily hydrolyzed to the corresponding aryl mercaptans to give thiophenols. In reporting on their research, they show that when O-(2,4,5-thrichlorophenyl)-N,N-dimethylthiocarbamate was heated to 220.degree. C, there was obtained the corresponding S-(2,4,5-thrichlorophenyl)-N,N-dimethylthiocarbamate. Nowhere in their report do they show the thermal rearrangement of an O-(2,4,6-tribromophenyl)-N,N-dimethylthiocarbamate or of the analogous triiodophenyl compound to give the compounds herein discovered. The anomolous thermal rearrangement of the starting materials herein to give the product N-(5,7-dibromo-1,3-benzoxathiol-2-ylidene)-N-methylmethanaminium bromide or the corresponding diiodo iodide is nowhere obvious from Newman and Karnes.